Connecting a telephone line to a cellular unit requires connecting a central office switch of the public switched telephone network (PSTN) to a mobile telephone switching office (MTSO) which in turn is connected to radio equipment, via message signal and control signal processing and switching equipment. This arrangement with its varied circuitry and systems has typically been positioned and packaged rather diversely. Changes to the system have required significant modifications to the wiring and replacement of many individual component packages.
Cellular radio telephone systems operating specifications, related to system aspects including message and data signal processing, are governed by regulatory agencies whose mandated standards are constantly changing. Any change in these standards, such as a change in protocol requirements, almost automatically means a significant change in the switching and processing circuitry used in the cellular telephone system. Modifying the present equipment to meet the new standards can mean extensive changes to many individual component units and system packages.